Flow over a hydrofoil in the wake of a propeller

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Large Eddy Simulations are reported on the flow around a rudder operating in the wake of a propeller. Results demonstrate the production of important spanwise flows within the boundary layer on the hydrofoil, mainly tied to the behavior of the largest coherent structures populating the propeller wake. The two branches of the hub vortex are shifted from the pressure towards the suction sides of the rudder. The pressure and suction side branches of the tip vortices move outward and inward, respectively. This phenomena increase the asymmetry between pressure and suction sides, with wider areas of the rudder surface affected by the propeller wake on the pressure sides. In the vicinity of the leading edge the main sources of turbulent fluctuations within the boundary layer on the hydrofoil are the two branches of the hub vortex, with also an evident signature of the tip vortices, especially on the suction sides, where they experience a stronger stretching. Moving from the leading edge towards the trailing edge both momentum and turbulence within the rudder boundary layer become obviously higher on the pressure sides than on the suction sides, because of the impingement operated by the propeller wake, whose azimuthal velocity is directed towards the pressure sides of the hydrofoil. Such effect is evident across the whole spanwise extent affected by the propeller wake, involving also the outer radii populated by the tip vortices. However, moving away from the surface of the hydrofoil the turbulent stresses become higher on the suction sides, due to the shear generated by the contraction of the propeller wake, which is instead expanding on the pressure sides.